The most ubiquitous pollutant found in air is CO; the CO danger is well known in home, workplaces and vehicles. Over 1100 people lose there lives do to carbon monoxide (CO) generated by vehicles annually according to the Cobb and Etzel JAMA Aug. 7, 1991 Vol. 266, No. 5. According to the EPA's “Air Quality Criteria for Carbon Monoxide” Published in 2001 on the Internet, stated that 3.75 million workers are exposed to dangerous levels of CO in the workplace from engine exhaust in just one year. The Center for Disease Control experts Cobb and Etzel found that over 5,600 people are recorded to die from CO according to the death certificates database. Michael Dolan states that these fatalities are grossly underestimated. He found that 23.6% of those people diagnosed with the flue by doctors actually had CO poisoning. This work by Dolan and others (Heckerling) demonstrated that CO poisoning is poorly diagnosed by doctors. Therefore there is a need for more accurate and reliable CO sensors.
In 1993, according to the National Highway Safety Traffic Administration (NHSTA) over 100 people lost their lives as a result of CO while the vehicle is moving. Princess Diane's driver was poisoned with CO as proven by a test on his blood indicating, i.e., about 20% carboxyhemoglobin (COHb). The CO poisoning was discovered because of the exceptional attention given to this case.
Goldstein and another described one example of a CO sensing means by Goldstein et al. Both disclosed biomimetic sensors in U.S. Pat. No. 5,063,164 and U.S. Pat. No. 5,618,493, the contents of which are incorporated by reference. These biomimetic sensors mimic the human response to CO. This chemistry was an improvement of an earlier invention by Shuler and Schrauzer, i.e., U.S. Pat. No. 4,043,934. The Shuler and Schrauzer Patent also teaches the use of a chemistry with high copper ion concentration to convert CO to carbon dioxide even at room temperature. Shuler Schrauzer catalyst has limited life and operates over a narrow range of relative humidity and is not very effective compared to the 10K catalyst as shown by the comparative data.
U.S. Pat. No. 5,063,164 teaches that in the presence of the CO gas the level of danger from the hazardous exposures may be determined by monitoring the sensor with a photon source. By passing photons of a specific spectral region through the sensor and monitor the intensity of the photon beam or use a pulsed photon source to conserve power such as an infrared LED combined with a simple photon detector such as a photodiode. There are a number of other gas sensors that have been disclosed in the following U.S. Pat. Nos., e.g., 4,043,934, 5,346,671, 5,405,583, 5,618,493 and 5,302,350, which can detect a target gas such as CO by monitor the optical properties of the sensor.
Goldstein described several CO detector systems, which incorporate these types of optical changing sensors. For example, the biomimetic sensor was discussed in U.S. Pat. Nos. 5,280,273, 5,793,295 and others such as by Marnie et al disclose a low cost circuit (Apparatus) with software and method for detecting CO in U.S. Pat. Nos. 5,573,953 and 5,624,848. Goldstein et al further disclosed a digital and rapid regenerating means in co-pending patent applications Ser. Nos. 60/051,038, 80/026,34 and 60/076,822 herein incorporated by reference. The gas detector system includes a housing containing photon sources, which emits photons in at least a region of the electromagnetic spectrum that the sensor absorbs in response to the CO exposure. A photodetector sensitive in the corresponding active region of the spectra a circuit designed to measure the response and a noisemaker or other signaling means is used. The signaling means is actuated by circuit and software system. The housing (enclosure) has at least one opening to permit the sound to escape and the entry of CO or other gases. The detector also contains a sensor, which may be a permanent type sensor or may be configured with a battery for convenient replacement or may be mounted within the housing designed for easy replacement. Several systems are disclosed in U.S. Pat. No. 5,793,295 by Goldstein issued in Aug. 11, 1998 and is hereby incorporated by reference. Goldstein also described in Aug. 11, 1998 patent U.S. Pat. No. 5,793,295 a CO/smoke detector that increases sensitivity of smoke in the presence of CO. The new novel Co/smoke has a light trapping system, which comprises curved fins of black plastic so that smoke has easy access from all directions. This is an improvement over the Co/Smoke alarm described in U.S. Pat. No. 5,793,295 in which a dropping resistor is used to enhance the air flow through the smoke chamber with a heating chimney effect. Therefore the new device is useful for battery power; AC power; 12-volt low power system as well as AC with battery back up. These combinations and multiple sensing fire detection systems may function better with two K series sensors each in a separate chamber. Although the edge-looking view with the S34 with 20 percent spike of silicomolybdic acid and paladium was shown to be quite fast at 550 ppm with alarm time of 20 seconds or less, they cannot detect 20 ppm in 2 minutes, which is important for fire detection.
The cross fertilization fire detectors has not been commercialized yet although it was designed, the S sensor cannot be made both sensitive enough to detect a 20 ppm CO rise above ambient without false alarms and have a reasonable life. The slower speed of the S sensor makes it difficult for a system to fix the exact location of the CO rise and then compare it with ambient conditions. The near instant response of the K sensor is ideal for larger system in which it is possible to compare the rise of one or two sensors with appropriate software as discussed above and below. The K sensor is expected to last longer than the circuit, which is estimated at 10 years maximum with high confidence. Therefore, this novel CO-smoke is much more practical and useful than other CO smoke detectors. Currently First Alert is marketing a combination CO detector, which contains the Quantum S34 sensor and software. The new K sensor allows the manufacture of a lower cost, better performing CO smoke detector.
Several low-cost biomimetic sensors are disclosed in U.S. Pat. Nos. 5,063,164, 5,624,848 (Marnie et al), systems U.S. Pat. No. 5,618,493, (Goldstein et al), U.S. Pat. No. 5,280,273 (Goldstein), U.S. Pat. No. 5,793,295 (Marnie et at). These software systems will not work with the K series sensors. Higher performance advanced systems are disclosed in co-pending applications Ser. No. 60/076,822 filed Mar. 4, 1998 and a digital CO detector PCT/US97/16846 Filed 19 Sep. 1997 the contents of which are hereby incorporated by reference. The new K sensor with catalyst and dummy catalyst system can meet the needs of the market place.
The above K series CO sensor catalyst technologies may be incorporated into the small size CO detector or digital monitor. The K series cat-sensor is excellent for use in ventilation controls, medical devices, fuel cells and digital monitors as well as fire alarms.
In addition, the customer may incorporate the K-series sensor and operating circuitry into an automobile before it is purchased. This CO and other gas safety device may be incorporated in the passenger cabin or elsewhere in the vehicle. In some cases, a dual sensor system may be used so that a “smart” vehicle can protect its passenger from the effects of CO containing smog in the outside environment as well a vehicle generated CO. There may be one sensor inside and a second sensor outside the cabin. When the outside is indicates higher levels than inside the vents can be shut (and the windows closed) the air re-circulated, optionally through a catalytic means to convert the CO to carbon dioxide. The catalyst is described below.
Several Low cost embodiments of this invention incorporate one cat-K and one dummy-K sensor, a low power consuming sensor monitoring system used for detecting the presence of a predetermined carbon monoxide (“CO”) concentration and humidity.
These sensors comprise at least one self-regenerating sensing reagent coated onto a substrate, for example, a high surface area transparent material such as a porous glass, sol-gel silica or SPS (silica porous substrate manufactured by Quantum Group by a trade secret process. The SPS substrate consist of a porous solid silica material, which is sufficiently transmissive to a specific range of photons in the specific wavelength region to interest, i.e., visible and near IR. The SPS substrate is coated with the K sensor material by a self-assembly process. The K sensor is used to detect the optical characteristic changes in the sensor using an optical source such as a light emitting diode and a photodiode. These optical components and sensor(s) are controlled by a circuit designed to measure the output of the photodiode monitoring the sensor which would alert the passengers through some means and actuate controls as programmed depending on the level of hazard or condition.
Another embodiment is a modification of embodiment 1, e.g., based on dI/dt Plus IK, where I is equal to the intensity of photons and K is a constant. Under certain conditions the derivative of the transmitted photon with respect to a time interval plus the actual transmitted photon intensity is proportional to the carbon monoxide (CO) concentration,[CO]=k1{dI/dt}+I(K2) at other times[CO]=k2 {I(n)}When dI/dt is very near zeroand when dI/dt is not linear such that the second derivative is not very near zero then the sum of the two, i.e., I(n) and dI/dt is divided by 2 or by an average or mean, in addition a weighted average is feasible such as represented by the general equation:[CO]=c{k1[dI/dt]+k2[I(n)]}
The approximation can be employed easily and can limit the cost of the alarm or detector and has the capability of digital display.
Other approximations are also possible, e.g., the sum of averages or weighted averages over a series of registers[CO]=kl(dI/dt)+K2[I(n)]
There are two basic optical techniques that can be incorporated as embodiments of the optical monitoring method, i.e., 1) transmission as discussed above and 2) reflection a second embodiment of this invention.
Let us describe the photon transmission method, as it is generally preferred. This method can be used for a variety of gases for which a similar responding optical sensor exists; however, as an example carbon monoxide (CO) will be discussed as the target. by this exemplary focus on CO we in no way intend to limit the target gases of this method. This method maybe useful in producing digitally displayed CO concentrations.
A third embodiment of the invention is a fixed point detector (which has been calibrated to go into alarm or warning when the sensor optical properties change past some point that is preset during calibration) and measure the sign of the derivative dI/dt to know when to stop alarming.
In the absence of CO concentration above the threshold concentration, which is defined as 2000 ppm for the 2K sensor, the K series sensor will operate properly unit it reaches or exceeds the threshold. The system can use more than one sensor, e.g., if the 2K is exceeded the monitor can be automatically switch over to a 5K sensor and so as needed. Only one reference sensor should be needed.
Most of the current portable digital gas detection products with acceptable accuracy (plus or minus 2%) on the market are battery operated and use electrochemical cells for sensors. Units that are accurate are expensive, typically $500 to $1000, require frequent calibration, and frequent sensor and battery replacements. These electrochemical units can not operate at −40° C. nor can they live for long periods of time at 70° C. Metal oxide Semiconductor sensors take very large amounts of power and therefore cannot be operated for a reasonable time of 2 years on a small 9 volt battery. The MOS sensors are subject to interfering gases and also lose sensitivity when exposed to silicones often used in the automotive industry. Therefore there is a need for a low cost, reliable, low power, accurate, easy to use battery powered unit to detect various gases such as CO especially a unit that can be incorporated in an automobile or other vehicles. There is a need to incorporate the product into new fire detectors because 70% of all fire deaths are CO related.
The K series sensor operates from temperature ranges from minus 40° C. to +90° C. and from nearly zero to 100% relative humidity, when the reservoir system is employed.
Acid gases such as sulfur dioxide, sulfur trioxide, oxides of nitrogen, and similar acid compounds may be removed from the air stream by means a getter comprising a porous air filter mater impregnated with acid reacting chemical such as sodium bicarbonate, sodium carbonate, calcium carbonate and magnesium hydroxide. In addition, a filter section or getter may be designed to react with bases such ammonia. Getter may consist of citric acid, tartaric acid, phosphoric acid, molybdosilicic and other acids such as phosphoric, polymeric acids impregnated on silica gel or other suitable substrate such as felt. The preferred embodiment of the ammonia getter is the subject of a co-pending application Ser. No. 60/110,898 filed Dec. 4, 1998 by J. Ryu and Paula Johnson. A layer of charcoal may separate the acid from the basic layer, A useful air purification system may include 4 to 5 active layers separated by inert material such as a porous felt. The air purification system is also the subject of a co-pending application Ser. No. 09/105,544 filed Jun. 26, 1998.
One skilled in the art may appreciate a low powered CO sensing control apparatus which can also measure and display digitally the gas concentration by calculations from the response of optically responding RH and CO+RH sensors. Currently, there are no selective digital CO detection products that can operate for many years with common batteries such as 9-volt alkaline. Such an apparatus and method would increase the desirability of a wide variety of products from home safety detectors to personal monitors, medical products, breath diagnostics to industrial controls to automotive gas sensing products, to safety shut off systems for appliances and controls for ventilation systems.